Method of manufacturing a motor core

ABSTRACT

A method for manufacturing a motor core having a plurality of metallic plate-like laminations includes the steps of a) juxtaposing the laminations in a stacked relation, b) placing the laminations over an alignment post of an alignment fixture, c) flowing at least one bead of hardenable adhesive material along the outer peripheral surface of the laminations where the adhesive material, when cured, fixes the laminations in a predetermined non-moving orientation, d) removing the laminations from the alignment fixture; and e) applying windings to the laminated stack.

FIELD OF THE INVENTION

The present invention relates generally to motor cores and stators andmore particularly to a method of manufacturing a motor core byadhesively bonding laminated layers without applying compression to thelayers.

BACKGROUND OF THE INVENTION

Motor cores are generally composed of many layers of thin metal platesthat are stacked on top of each other to form a laminated stack.Typically, the laminated stack is fastened with welds, rivets, or boltswhich hold and/or compress the layers together to permanently maintainthe stack in a fixed orientation. Stator windings are then fitted aboutor wound in place about grooves or slots formed in the inside peripheralsurface of the laminated stack to form poles of the motor. Duringprocessing of the metal plates and prior to assembly, the plates areannealed to form an oxide layer on the surfaces of each metal plate. Theoxide layer effectively insulates one plate from the adjacent plate,provided that the plates are not subject to significant compression. Useof rivets or bolts that compress the stack “shorts-out” the oxide layercausing some or all of the metal layers to be electrically coupled toadjacent layers, essentially “short circuiting” the stack forming aconductor. Welding the layers together similarly creates a short circuitbetween the plates. In some motor applications this is acceptable, andeven desirable.

However, in other motor applications, this is not acceptable, as shortedplates reduce the efficiency of the motor by increasing eddy currentloss in the stack. In such applications, the metal layers must beelectrically isolated from adjacent layers. Such stacks are referred toas “loosely laminated” stacks because the metal plates are not subjectto significant compressive force. Typically, applications requiring aloosely laminated stack are directed toward smaller motors, such asfractional horsepower motors in the range of one-half to one horsepower.However, some loosely laminated stack motors may be as large as fivehorsepower. The loosely laminated stack must be fixed so as to preventthe metal plates from becoming skewed while simultaneously avoidingdetrimental compressive force.

It is known to use clamps to hold the plates in position while thewindings are attached or wound about the slots or grooves in the stack.This is costly and labor intensive, and care must be taken not to applytoo much compressive force. Application of too much compressive forceresults in shorting some or all of the laminations, while application oftoo little compressive force permits the plates to move, resulting inair gaps between the laminations and skewed laminations. Accordingly,use of clamps is disadvantageous in the manufacturing of looselylaminated stacks.

In some applications, large clamping or compressive force is used inconjunction with a chemical adhesive. Of course, a loosely laminatedcore cannot be manufactured in this way. Such methods use slow-curingadhesives that require the core to remain under compression forrelatively long periods of time while the adhesive hardens. Applicationof such compressive force may involve expensive and bulky fixtures andis an inefficient use of manufacturing floor space. Also, such methodsusing adhesive are disadvantageous if large compressive force is notused. Without use of substantial compressive force, the cores may sufferfrom lack of rigidity and lack of squareness if the glue is notpermitted to harden, undisturbed, for a relatively long period of time.Therefore, compression of the core is required during this time toinsure dimensional accuracy. As described above, such compression causesshorting between the layers, thus this method cannot be used to produceloosely laminated cores.

It is also known to provide a cylindrical bore through the stack that isfilled with a chemical adhesive, which when dry, bonds the layerstogether. Again, this is expensive and time consuming. In known methods,it is difficult to keep all of the metal layers aligned. Failure tomaintain alignment between the metal layers results in “skew,” whichseverely reduces the efficiency of the motor, thus affecting motorperformance. Skewed motor cores are unacceptable.

SUMMARY OF THE INVENTION

It is therefore desirable to provide a loosely laminated stack and amethod of forming the loosely laminated stack. The cost of manufacturingthe loosely laminated stack is significantly reduced because complex andbulky jigs and clamps are not required to hold the laminations in place.Further, there is no expensive welding operation required and no bolts,rivets, or other mechanical fasteners are used. This reduces materialand labor costs. Quality control costs are similarly reduced because thelaminations are not subject to significant compressive force. Thisresults in fewer rejections due to shorted laminations.

In the present method, the operator need only place the laminations overthe alignment post and flow several beads of adhesive material along theoutside surface of the laminated stack. The adhesive material cures andhardens in only a few seconds. Accordingly, the laminated stack, oncealigned and fixed in place by the adhesive, is ready for the windingprocess.

More specifically, a method of manufacturing a motor core having aplurality of metallic plate-like laminations includes the steps of a)juxtaposing the laminations in a stacked relation along a central axis,the laminations having a central aperture and an outer peripheralsurface, b) placing the laminations over an alignment post of analignment fixture to align the laminations, until the laminations restupon a base portion of the alignment fixture, where the alignment posthas an outside diameter substantially equal to an inside diameter of thecentral aperture so as to form a slip fit therebetween to urge thelaminations into full alignment, c) flowing at least one bead ofhardenable adhesive material along the outer peripheral surface of thelaminations in a generally vertical orientation between a top laminationand a bottom lamination where the adhesive material, when cured, fixesthe laminations in a predetermined non-moving orientation, d) removingthe laminations from the alignment fixture; and e) applying windings tothe laminations. Other features and advantages of the invention willbecome apparent from the description that follows.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a laminated stack and an alignmentfixture;

FIG. 2 is a top plan view of the laminated stack and the alignmentfixture of FIG. 1; and

FIG. 3 is a side elevational view of the laminated stack and thealignment fixture of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-3, FIG. 1 shows a specific embodiment of alaminated stack or motor core 10 disposed over an alignment post 12 ofan alignment fixture 14. The alignment fixture 14 includes the alignmentpost 12 fixed to a base portion 16 at a ninety degree angle. Preferably,the alignment post 12 is disposed in the center of the base portion 16and may be integrally formed with the base portion, or it may beremovable. The alignment fixture 14 is formed of hardened steel, toolsteel, or other suitable durable material. The alignment post 12 has aslightly tapered or rounded distal portion 18 that facilitates initialalignment and orientation of the laminated stack 10 over the alignmentpost. Two oppositely disposed keys 19 extend axially along the surfaceof the alignment post 12. Placing the laminated stack 10 over thealignment post 12 eliminates skew between the layers 20 and aligns thestack, as will be described below.

The laminated stack 10 is formed of many layers of metallic plate-likelaminations or layers 20 having a thickness of about 0.025 inches,hereinafter interchangeably referred to as layers, plates, orlaminations. However, depending upon the motor construction, thedimensions of the layers 20 may vary in thickness, width, and generalsurface area con figuration. As best shown in FIGS. 1 and 3, thelaminated stack 10 includes an upper or top lamination 22 and a lower orbottom lamination 24. Each layer or plate 20 is generally circular inshape having a central aperture 30. Each lamination 20 preferablyincludes two flat portions 34 forming chord-like surfaces on an outerperipheral surface 36 when the laminations are stacked. However, anysuitable number of flat portions 34 may be included. As best shown inFIGS. 1-2, the laminated stack 10 includes a plurality or U-shapedgrooves or slot openings 38 disposed about the central aperture 30. Theslot openings 38 form corresponding slot tooth portions 40 about whichcopper wire is wound to form the winding (not shown) of the motor core10.

In operation, the plurality of the metal plates 20 are stacked in ajuxtaposed relation such that the slot openings 38 are aligned along theentire height of the laminated stack 10. The stacked laminations 20 arethen placed over the alignment post 12 such that the alignment post isreceived within the central aperture 30. The slot openings 38 areinitially aligned so that when the laminated stack 10 is placed over thealignment post 12, the outwardly projecting keys 19 engage correspondingslot openings so as to maintain each plate 20 in the same orientationrelative to an adjacent plate. This eliminates skew. Preferably, thealignment post 12 includes two keys 19, however one or more keys may beused. The laminated stack 10 is placed over the alignment post 12 untilthe stack rests on the base portion 16 of the alignment fixture 14. Thebottom layer or plate 24 directly contacts the base portion 16 and isparallel to the base portion such that there is no “wobble” possible.Accordingly, a central axis of the motor core 10 is exactly square tothe base portion 16 and coincident with a central axis of the alignmentpost 12. The rounded or tapered distal portion 18 of the alignment post12 facilitates quick and convenient reception of the alignment postwithin the central aperture 30.

The alignment post 12 has an outside diameter substantially equal to aninside diameter of the central aperture 30. Hence, a loose slip fit isformed between the alignment post 12 and an inside surface 42 (FIGS.1-2) defined by the central aperture 30. The force directed against theinside surface 42 tends to urge each of the metal layers 20 intoalignment along the entire height of the laminated stack 10. Becauseeach layer 20 is identical in size and shape, once the layers arealigned, the outer peripheral surface 36 of the laminated stack 10 andthe inside surface 42 form a uniformly smooth curved surface. Thus, thealignment post 12 facilitates vertical alignment of the stack 10 whilethe keys 19 facilitate “rotational” alignment between adjacent layers20. Alignment of the layers 20 eliminates skew therebetween. As will bedescribed below, use of a chemical adhesive facilitates maintainingalignment without requiring the application of compressive force.Because substantially no compressive force is applied, clamps, jigs, andequipment usually required to apply compressive force are eliminatedthereby reducing production costs and increasing efficiency.

Once the laminated stack 10 is placed over the alignment post 12 suchthat all of the metal layers 20 are aligned, a bead of hardenableadhesive material 50 is flowed along the flat portion 34 of the outerperipheral surface 36. The bead 50 is flowed in a generally verticalorientation between the top lamination 22 and the bottom lamination 24.Preferably, two beads 50 are applied to each flat portion 34 at oppositeedges thereof. Of course, any suitable number of beads 50 may be applieddepending upon the dimensions of the motor core 10 and the relativedimension of the flat portion 34. Alternately, the motor core 10 may becompletely circular in shape, as seen in a top plan view, having no flatportions 34. In this case, the beads 50 are simply flowed along theouter peripheral surface 36 of the laminated stack 10 from the toplamination 22 to the bottom lamination 24 along the curved outerperipheral surface 36. The beads 50 additionally wick between thelaminations 20 to further adhere one plate to an adjacent plate.

The beads of adhesive 50 are applied via a tapered nozzle 52 (FIG. 3)that limits the amount of adhesive applied. Due to the specific natureof the chemical adhesive described below, use of a small amount ofadhesive, rather than use of a large amount of adhesive, results in astronger bond. Additionally, use of a relatively small amount ofadhesive results in reduced manufacturing costs.

The bead 50 of chemical adhesive is a cyanoacrylate adhesive material orother suitable fast curing adhesive. The chemical adhesive may be soldunder the name of SUPERGLUE or LOCKTITE 420. The adhesive hardensrapidly, typically within ten seconds. Such adhesives are often referredto as rapidly-curing or instantly-curing adhesives, and may harden inabout five to fifteen seconds. After the bead of adhesive 50 hashardened, the laminations 20 are fixed in orientation and cannot moverelative to each other. Note that the beads of adhesive 50 completelyretain the core 10 in an aligned orientation to provide dimensionalaccuracy and rigidity in the completed core 10. Vertical and rotationalalignment (skew) of the layers 20 is achieved solely through use of thechemical adhesive and the simple alignment fixture 14, without the needfor complex jigs, clamps, or other devices used to apply compressiveforce to the core 10.

Use of an instantly-curing cyanoacrylate adhesive eliminates the needfor the core 10 to remain on the alignment fixture 14 for an extendedperiod of time. Methods using slow-curing glue either requirecompressive force to be applied and/or require that the core 10 remainon the fixture and immobile for a relatively long period of time whilethe adhesive hardens. This results in inefficient use of themanufacturing facility and also requires use of many such fixtures tomeet production demands.

After about ten seconds, the fast-curing adhesive has hardened and thecore 10 is removed from the alignment fixture 14. At this time, MYLARinsulating sheets or wrappings (not shown) are placed within the slotopenings 38, and the windings (not shown) are wound about the slot toothportions 40. Lead wires (not shown) are then connected and the completedcore 10 is varnished.

What is claimed is:
 1. A method of manufacturing a motor core having aplurality of metallic plate-like laminations, the method comprising thesteps of: juxtaposing the laminations in a stacked relation along acentral axis, the laminations having a central aperture and an outerperipheral surface; placing the laminations over an alignment post of analignment fixture to align the laminations, until the laminations restupon a base portion of the alignment fixture such that substantially nocompressive force is applied to the laminations; the alignment posthaving an outside diameter substantially equal to an inside diameter ofthe central aperture so as to form a slip fit therebetween to urge thelaminations into full alignment; flowing at least one bead ofcyanoacrylate adhesive material along the outer peripheral surface ofthe laminations in a generally vertical orientation between a toplamination and a bottom lamination, the adhesive material wickingbetween the laminations, and when cured, fixing the laminations in apredetermined non-moving orientation; removing the laminations from thealignment fixture; and applying windings to the laminations.
 2. A methodof manufacturing a motor core having a plurality of metallic platelaminations, the method comprising the steps of: juxtaposing thelaminations in a stacked relation along a central axis, the laminationshaving a central aperture and an outer peripheral surface; placing thelaminations over an alignment post of an alignment fixture to align thelaminations, until the laminations rest upon a base portion of thealignment fixture such that substantially no compressive force isapplied to the laminations; the alignment post having an outsidediameter substantially equal to an inside diameter of the centralaperture so as to form a slip fit therebetween to urge the laminationsinto full alignment; flowing at least one bead of cyanoacrylate adhesivematerial along the outer peripheral surface of the laminations while thelaminations are on the alignment fixture, in a generally verticalorientation between a top lamination and a bottom lamination such thatthe adhesive material wicks between the laminations; allowing theadhesive material to cure before removing the laminations from thealignment fixture, to cause the laminations to be fixed in apredetermined non-moving orientation; removing the fixed laminationsfrom the alignment fixture; and applying windings to the laminations. 3.The method of claim 1 wherein each lamination includes at least one flatportion forming a chord-like surface on the outer peripheral surface tofacilitate reception of the at least one bead of adhesive materialthereupon.
 4. The method of claim 1 wherein the at least one bead ofadhesive material is applied to the at least one flat portion of thelamination.
 5. The method of claim 1 wherein the at least one bead ofadhesive material is applied to the outer peripheral surface of thelamination.
 6. The method of claim 1 wherein the adhesive material is arapidly-curing adhesive material.
 7. The method of claim 1 wherein theadhesive material hardens in about five to fifteen seconds to facilitatefixing the laminations in an aligned orientation.
 8. The method of claim1 wherein the alignment post includes a tapered distal portion tofacilitate placement of the laminations over the alignment post.
 9. Themethod of claim 1 wherein the alignment post is disposed at a ninetydegree angle relative to the base portion of the alignment fixture. 10.The method of claim 2 wherein each lamination includes at least one flatportion forming a chord-like surface on the outer peripheral surface tofacilitate reception of the at least one bead of adhesive materialthereupon.
 11. The method of claim 2 wherein the at least one bead ofadhesive material is applied to the at least one flat portion of thelamination.
 12. The method of claim 2 wherein the at least one bead ofadhesive material is applied to the outer peripheral surface of thelamination.
 13. The method of claim 2 wherein the adhesive material is arapidly-curing adhesive material.
 14. The method of claim 2 wherein theadhesive material hardens in about five to fifteen seconds to facilitatefixing the laminations in an aligned orientation.
 15. The method ofclaim 2 wherein the alignment post includes a tapered distal portion tofacilitate placement of the laminations over the alignment post.
 16. Themethod of claim 2 wherein the alignment post is disposed at a